Ventrolateral prefrontal cortex is required for fear extinction in a modified delay conditioning paradigm in rats

Recent evidence has demonstrated that the ventromedial prefrontal cortex (vmPFC) is a critical site of the neural circuits underlying fear extinction memory. The ventrolateral prefrontal cortex (vlPFC) is not directly involved in extinction processes within the aversive domain. However, most of the current cumulated data on extinction is based on a classical delay fear conditioning paradigm in which the interval between the onset of the conditioned stimulus (CS) and the unconditioned stimulus (US) is consistent in a given protocol. In the present study, we developed a modified delay fear conditioning paradigm in which the temporal distribution of the footshock US during the duration of the tone CS is programmed to be pseudorandom. Here, we examined the effects of electrolytic vmPFC and vlPFC lesions made before training on conditioned fear response in the modified paradigm. The behavioral procedure involved four sessions with a 24-h interval: habituation, fear conditioning, extinction training, and extinction test. Percent freezing to tone was assessed as a measure of conditioned fear response. The results show that neither vmPFC nor vlPFC lesions affect acquisition or extinction of conditioned fear response during the fear conditioning and extinction training sessions, respectively. During the extinction test session, both vmPFC- and vlPFC-lesioned rats showed deficits in the recall of the between-session extinction memory. The deficits could not be attributed to altered nonspecific responses (footshock sensitivity, locomotor activity, and nonspecific freezing response). Furthermore, vlPFC lesions made before training had no effect on conditioned fear response in the classical fear conditioning paradigm. These data suggest a preserved role of the vmPFC in fear extinction and a selective involvement of the vlPFC in extinction process in certain fear conditioning tasks.